A. Field of the Invention
The present invention relates to a system utilizing on-chip microplasma discharges in a variety of applications, including for sources of light, for detecting and analyzing gas samples, and for detecting and analyzing contaminants in water. The present invention further relates to methods for utilizing on-chip microplasma discharges for generating light, methods for detecting and analyzing gas samples, and methods for detecting and analyzing contaminants in water.
B. Description of Related Art
Numerous efforts exist to utilize small scale on-chip plasmas (also referred to herein as microplasmas) for a variety of purposes, which may include microscale gas detectors and light sources. The present invention improves upon these efforts to present a reliable, affordable, and innovative system for generating light, including ultraviolet spectra, for detecting and analyzing gas samples, and for detecting and analyzing contaminants in aqueous solution.
Plasma-based discharges are used extensively for lighting in the macro-world, for example, neon bulbs and fluorescent lighting are ubiquitous as lighting sources, Small scale pyramidal discharge devices have been reported as micro-scale light sources, but these types of devices produce visible light only. In previous work, the present inventors developed a light source by striking a plasma discharge to metal-salt doped water in a microfluidic channel, see Mitra, B., et al. “Ultra-Violet Emission Source for Direct Fluorescent of Tryptophan,” Proc. Engineering in Medicine and Biology Soc., September 2003, pp. 3380-4; C. G. Wilson et al. “Profiling and Modelling of DC Nitrogen Microplasmas,” J. App. Phys., 94(5), September 2003, pp. 2845-51, each of which is herein incorporated by reference in its entirety. It is desirable to have an on-chip tunable light source that may operate within a vacuum and that may be used to fluoresce biomolecules and tagged DNA.
In the same manner, impurities or contaminants in water may be detected and analyzed using microplasmas, see C. G. Wilson et al. “Spectral Detection of Metal Contaminants in Water Using an On-Chip Microglow Discharge,” IEEE Trans. Electron Devices, vol. 49, No. 12, December 2002, pp. 2317-2322; C. G. Wilson and Y. B. Gianchandani, “Led-SpEC: Spectroscopic Detection of Water Contaminants Using Glow Discharges from Liquid Microelectrodes,” Proc. IEEE Conf. on MEMS, January 2002, pp. 248-51; and L. Que et al. “Microfluidic Electrodischarge Devices with Integrated Dispersion Optics for Spectral Analysis of Water Impurities,” J Microelectromechanical Sys., vol. 14, No. 2, April 2005, pp. 185-191, each herein incorporated by reference in its entirety. Such impurities or contaminants may be atomic (such as copper) or molecular (such as phosphorous and calcium). The latter lack large atomic spectral emission lines in the visible region, making them hard to detect by present means. Additionally, water impurities may also exist in small quantities such that detection is difficult. It is desirable to have an on-chip tunable device purporting to detect a broad range of impurities or contaminants in aqueous solution, including at small quantities, by utilizing a preconcentrator (for example, by evaporating the aqueous solution) and with the capability of operation at vacuum levels, used in combination with a spectrometer to detect and analyze water impurities or contaminants (see J. W. Sweeney and C. G. Wilson, “A Dusty Microplasma Spectroscopic Microdevice for On-Site Water Chemistry Analysis,” Louisiana Materials and Emerging Technologies Conference, October 2006, Louisiana State University, Baton Rouge, La.; J. W. Sweeney and C. G. Wilson, “Microdevices for On-Site Water Chemistry Analysis,” Louisiana Materials and Emerging Technologies Conference, December 2005, Louisiana Tech University, Ruston, La.; each of which is herein incorporated by reference in its entirety).
In addition to micro-scale light sources and water diagnostics, there is also presently a widespread need for the micro-scale detection of explosive gases, spanning from industrial safety to homeland security applications. Plasma emission spectroscopy is one of the most widely used forms of gas detection. However, direct current plasmas are typically preferred for atomic spectroscopy, not molecular spectroscopy, as red and infrared emissions are limited. Because magnetically confined plasmas have higher densities with lower electron energies, it is known that spectral emissions from molecular gases may be optimized by magnetically confining the microplasma. Previous efforts by the present inventors included magnetically enhanced microplasmas utilized to locally etch silicon (see “Miniaturized Magnetic Nitrogen DC Microplasmas,” IEEE Transactions on Plasma Science, vol. 32, No. 1, February 2004, pp. 282-287, herein incorporated by reference in its entirety). The ability to enhance the parameters of a direct current microplasma using micromagnets is a distinct advantage for developing inexpensive sensing devices on a microscale. Therefore, it is also desirable to utilize such micromagnets within an on-chip tunable gas detector that may operate in combination with a spectrometer to detect and analyze molecular gases in addition to atomic gases.